FR2500109A1 - Elastic coupling used between two mechanical parts, esp. tubes - consists of hollow ring made of corrosion-resistant polymer and filled with elastomer - Google Patents

Abstract

The coupling forms a seal resistant to attack by corrosive fluids; and consists of a ring with a U-shaped cross-section forming a cavity. The ring forms an external protective envelope resisting corrosion; whereas the annular cavity is filled with an elastomer made by adding a catalyst to a liq. resin. The ring is pref. made of PTFE; and is used esp. as a seal between two tubes, where one tube is inserted in the other. The smaller dia. tube pref. carries blocking rings which restrict the angle of bend at the junction between the two tubes. Instead of a ring, a PTFE cup contg. the elastomer may be used as a seal in a hole or a tube. Used in the preforming of blanks used to mfr. optical waveguide fibres, where the tubes are used to transport corrosive gaseous halides. The coupling precludes leakage.

Description

ELASTIC AND SEALED JUNCTION DEVICE
The present invention relates to a device for elastic and tight connection between two mechanical elements, at least one of these elements being hollowed out and containing a fluid.

 The tightness of the junction between two mechanical elements is very important especially when one of the elements blows a corrosive gas, and that one wants to eliminate any risk of leaks.

 In the case where the two elements considered are tubes, it is known to use a polytetrafluoroethylene lip seal. But there is a problem of wear of the seal when it is used in rotation. There are various other types of seals which have the following drawbacks: leaking corrosive gas, wear of the seal, complex handling, heavy weight and in this case the seal requires excessive support, cost and loss of time for implementation.

 In order to overcome these drawbacks, the present invention while allowing excellent sealing and temperature operation of the joint combines great ease of use and very low cost.

 The subject of the invention is an elastic and waterproof junction device resistant to the action of a corrosive fluid; this device comprising a body of circular shape, characterized in that this body comprises an outer protective envelope made of material resistant to this corrosive fluid, this envelope delimiting an open cavity of annular shape filled with an elastomeric material obtained by addition of a catalyst to a fluid resin.

The invention will be better understood by means of the description below and the appended figures among which:
- Figure 1 illustrates a device according to the invention
- Figure 2 illustrates a variant of the device according to the invention
- Figures 3 to 9 illustrate particular aspects of the device according to the invention;
- Figures 10 to 13 illustrate different types of possible seals used in the device of the invention
- Figures 14 to 19 illustrate other variants of the device according to the invention.

 This type of seal has been designed in particular for application on glass towers intended for the preform of optical fibers. In this particular case it is then a rotating joint.

 Figure 1 shows the simplest assembly. We consider two tubes 2 and 3, the ends of which are nested one inside the other. It is then considered that the alignment of the gas inlet tube 3 with that of the bore of the tube 2 is correct. In the particular case of the application on glass towers, this tube 2 is made of quartz. In the event of misalignment, a ball joint effect is created which, added to the internal pressure in the tube 2, tends to move the joint slowly. To remedy this defect Figure 2 shows the introduction of two stop rings 4 which by means of two protective washers made of polytetrafluoroethylene 5 make it possible to limit the stroke of the seal between two extreme points. Thus in this case when the 'the tube 2 is rotated around the axis A, there is no need for great adjustment precision, play is tolerated between the various elements threaded on the tube 3. In this particular case, illustrated in FIG. 2, the tube 3 fitted with the seal 1, the two rings 4 and the protective washers 5, comes to fit inside the quartz tube 2.

 In addition, this solution allows rapid assembly and disassembly of the assembly of the two tubes relative to each other, without risk of sliding of the seal threaded on the tube 3, the two rings therefore acting as stops in one way or the other as shown by the arrows in Figure 2.

 When the simplest assembly in FIG. 1 is carried out, that is to say when the end of the tube 2 of which the seal 1 is integral has been fitted on the tube 3, this tube 2 is rotated around the tube 3 which is the gas inlet tube. The tube 3 is made of stainless steel and the tube 2 of quartz, for example, the axis A being horizontal. This seal 1 ensures sealing between the gas inlet tube 3 and the tube 2 while resisting attack caused by the gases used which are in particular hallides.

 The seal 1 is illustrated in FIG. 3, it consists of two elements, the casing 6 and the regulator 7.

 Indeed, this seal 1 is a body of circular shape which has been hollowed out around its periphery to form an open cavity of annular shape, a polymerizable elastomeric material with high elasticity being introduced into this cavity; this material forms the regulator. The envelope is therefore the outer part of the joint. It is made of a material with high chemical resistance to corrosion. In addition, this envelope is flexible and deformable to adapt perfectly thanks to the regulator, to the inner enclosure of the tube 2 and to the tube 3. Thus to take account of these different conditions, this envelope is made of polytetrafluoroethylene. This makes it possible to work in difficult conditions, since this seal is in the presence of corrosive gases under pressure. it is subjected to a high temperature due to the proximity of a torch which sweeps the length of the tube 2 located beyond the joint 1, in the particular case of manufacturing optical fiber preforms. In this case due to the rotation of the tube 2 there is creation of another source of heat due to the friction of the rotating parts. A pronounced misalignment may exist between the fixed part and the mobile part; in fact, these tubes are produced with wide manufacturing tolerances.

 However, polytetrafluoroethylene has a particularly remarkable chemical inertia. It is resistant to almost all chemicals and does not dissolve in any solvent.

 It can be used up to 2800 C. In the case of permanent friction, the maximum linear speed is 50 meters / minute. Beyond this, the low thermal conductivity can cause a hot spot on the surface which may exceed the decomposition temperature.

 Under the action of a load, polytetrafluoroethylene deforms first and then tends to stabilize. This property is designated by the name of "creep". Its coefficient of friction is extremely low: it is for example 0.04 on polished steel, and it is self-lubricating and non-stick. By comparison, used under the same conditions, rubber or neoprene have coefficients of friction of approximately 0.8.

 The regulator 7 is located in the machined cavity inside the seal. It is not in contact with corrosive gases. It is made of a material with high elasticity in compression, which allows after polymerization to regularize the pressures exerted on the envelope during the introduction of this seal inside the tube 2 then during the introduction of the tube 3 inside the assembly formed by this joint and the tube 2 to produce the actual junction. This regulator makes it possible to control and distribute the deformations of the envelope as well as possible, the degree of crushing of which it controls, thus allowing the creep to stabilize.

 This regulator can be a silicone elastomer, for example "silastene". The "silastene" is in the form of a fluid resin which after addition of a catalyst in liquid form vulcanizes at ordinary temperature to give an elastic and resistant product. In addition it molds very easily, it remains elastic up to a temperature of 2500 C, it resists humidity and aging and has good heat conductivity. It also has a high coefficient of friction: around 0.8.

 If we consider Figures 4 and 5 which represent the operations carried out to effect the junction between the two tubes 2 and 3. The outside diameter of the joint is greater than that of the inside diameter of the tube 2.

Fitted into it, the seal 1 then undergoes a diametrical stress which has the effect of compressing the volume containing the regulator 7, the pressure inside the envelope 6 increases. Thus the central zone shrinks by deformation. There is thus a part of the overflow elastomer 9a. If the tube is then removed, the elastomer returns to its position because of its elasticity under compression, and because of the internal curvature of the envelope; this internal curvature having the aim of retaining the elastomer by adhesion to the internal walls.

 If after having inserted the seal into the tube 2, the tube 3 is introduced therein, the cavity volume shrinks by lateral deformation and the seal adapts with a certain pressure to the external wall of the tube 3. The junction seal is thus assured. The overflow elastomer part 9a then increased and becomes 9b.

 There is a pressure balance which is created, with a stabilization of the creep.

 This overflow of the regulator is more or less accentuated, depending on the tolerances for producing the bore of the lateral tube 2 and of the central tube 3.

 It is also possible to play on the importance of this overflow in order to increase the tightness of this joint.

 As indicated above when it is dismantled, this seal decompresses and the overflow of the regulator reintegrates the envelope thanks to the arched shape of the interior thereof. And the joint returns to its original dimensions, ready to be reused.

 FIG. 4 therefore represents the seal 1 fitted at the end of the tube 2. The compression of the seal is distributed via the regulator. This joint, which fitted onto the tube 3, either freely or by means of a slight axial thrust, according to manufacturing tolerances, now has its internal diameter significantly smaller than the external diameter of this tube 3.

Tube 3 is then threaded into this joint. This operation is carried out without any difficulty, and the overflow of the overflow zone 9a then becomes 9b.

 This type of joint works both in rotation and in translation, as well as in a ball joint, but these various movements can also be simultaneous.

 The seal has the shape of a hollow cylinder, the side wall of which has a convexly curved bulge. This shape of the joint allows it to be fitted into its housing without difficulty. It also promotes the patella effect.

It allows, as shown in Figure 6, radial misalignments and especially significant angular misalignments 10, for example of the order of 10 degrees relative to the axis
The invention makes it possible to obtain a minimum linear speed of the dynamic part of the rotary joint in this case under the best conditions; this joint 1 rotating around the outer wall of the tube 3, due to a friction torque to overcome which is less. In addition, the type of joint considered has minimum diametrical dimensions in consideration of the two tubes which must be joined. This peculiarity is very important in the case of a glass lathe, in fact the joint, which makes the junction between two tubes which rotate relative to each other, rotates continuously for hours: this speed of rotation is , for example, of 1 turn per second. And it is important to minimize the causes of temperature rise which may hasten the process of decomposition of the joint.

We can also consider a thin polytetrafluoroethylene tape. I1 is this thin tape used in particular for sealing the joints of water circuits. Wrapped around the joint, it increases its diameter. The seal can then:
- either be used in a larger diameter tube;
- either be used in a tube of normal tolerances. Compressing the regulator more, thus reducing the diameter of the seal core, which has the effect of increasing the seal, or making up for a too large difference in diameters between the bore of the seal and the gas inlet tube .

 We can also consider several seals mounted in series as shown in Figure 7. This arrangement shown in Figure 7 allows to control an increase in sealing; the adjustable distance 11 between the 2 stop rings 4 making it possible to modify the compression of the opposing elastic elements 12 and 13 whose effect is reflected on the casing 6.

 The assembly and disassembly of the seal can be facilitated by the introduction of the 2 locking rings 4 integral with the tube 3. But there is another method requiring no intermediary. It suffices to give a rotation movement to the tube 3 while pulling along 14 to take out the seal or to push along 15 to fit it as shown in FIG. 8. These rings 4 can be rings of a type particular as illustrated in 13 figure 9. Indeed the smallness of the space receiving the seal led to the study of a new type of locking ring in stainless steel, easy to use and capable of strong adhesion on the polished part of the gas inlet tube 3, without damaging it. This locking ring comprises a ring open on a first notch (23), a second notch 22 forming with this first notch a movable part (19). The adjusting screw 18 located in a cavity that this ring has allows to press obliquely on the movable part 19, flexible relative to the hinge 20. The lever arm 21 is thus important, the pressure is therefore higher and the better wrap on the tube. On the other hand the width of the slot 23 is calculated so as to avoid the risk of permanent deformation, likely to reduce the bore of the ring. This would have the effect of #raying the polish of the tube during the fitting of the seal.

 When this joint 1 has exceeded its elastic limit, that is to say when the polytetrafluoroethylene is in a zone of permanent deformation, another possibility appeared: this joint can be reshaped. The joint thus obtained retains its shape characteristics, it is reduced in diameter and increased in length, while retaining its intrinsic qualities; the regulator adapting to this modification of the shape of the envelope. This allows re-use of seals with a core diameter made too large, by wear for example, or for adaptation on an end of the gas inlet tube too reduced in diameter after a return to the lathe followed by a polishing.

 This joint can be used with an oval tube 3, as long as the peripheral contact with the internal wall of the tube 2 is fully ensured and the junction is well made. It is the same with an ovalized tube 2.

 The machining of the envelopes is simply resolved. To avoid that the pressure of a tool on a too thin and too elastic wall deforms it, the tool no longer biting, we use the consolidating role of the elastomer by first making a blank in polytetrafluoroethylene, with a bore central and an annular cavity; this cavity is then filled with elastomeric material ("silastene") and it is only then that the external curvature is machined.

 There are different types of possible joints. The joint shown in Figure 10 allows large amplitude oscillations. The seal of Figure 11 has a radius of curvature inward, thus allowing greater adhesion to the inner wall of the outer tube. The joint of Figure 12 is self-aligning with strong peripheral adhesion due to the high coefficient of friction of the material forming the regulator and increased sealing. The joint of FIG. 13 is a joint with external adhesion allowing small oscillations.

 It is also possible to solve problems of sealed rotation. FIG. 14 illustrates a joint with lower adhesion, and FIG. 15 a joint with lateral adhesion. In this second case, the guidance is better. In these two cases, the seal is inserted between the two opposite cylindrical bearing surfaces which the two mechanical elements 30 and 31 comprise which rotate relative to one another.

 This type of rotating joint can just as easily be used as a waterproof cover; by producing a full cylinder, the wall of which has a convex curvature bulge. A sealed junction of a cylindrical orifice can be made by means of its side wall or the bottom of its envelope. Figures 16 and 17 show plugs; gripped by the protruding elastomer part with regard to FIG. 17.

 These joints can be fitted in a cup and are axially mobile. In FIG. 18, a piston-type seal has thus been produced.

 Finally, a seal of this type can serve as a plug to close an orifice, as in Figure 19.

Claims (13)

 1. Elastic and waterproof junction device resistant to the action of a corrosive fluid; this device comprising a body (1) of circular shape, characterized in that this body (1) comprises an outer protective envelope (6) made of material resistant to this corrosive fluid, this envelope (6) delimiting an open annular cavity filled an elastomeric material (7) obtained by adding a catalyst to a fluid resin.  2. Device according to claim 1, characterized in that this material with high chemical inertia is polytetrafluoroethylene.  3. Device according to claim 1, characterized in that two tubes (2, 3), inside which said fluid circulates, have one of their ends fitted into one another; and in that this body (1) forms an O-ring enclosing the outer tube (2) of larger inner diameter and being threaded by means of a light pressure outside the inner tube (3) of diameter weakest exterior.  4. Device according to claim 1, characterized in that two locking rings (4) are arranged on either side of this O-ring (1), threaded on an inner tube (3), a tube (2) of larger diameter then being entered outside of this joint.  5. Device according to claim 4, characterized in that each locking ring (4) is a ring open on a first notch (23), this ring comprising a second notch (22), these two notches forming between them a movable part (19), this ring comprising a cavity into which is inserted an adjustment screw (18) which acts on this movable part (19) to grip the tube (3) on which the ring has previously been threaded.  6. Device according to claim 5, characterized in that this locking ring (4) is made of stainless steel.  7. Device according to claim 4, characterized in that two washers (5) in polytetrafluoroethylene are arranged on either side of the O-ring (1), between this O-ring and each locking ring (4); the washers being threaded onto the inner tube (3).  8. Device according to claim 3, characterized in that the inner tube (3) is made of stainless steel, and that the outer tube (2) is made of quartz.  9. Device according to any one of the preceding claims, characterized in that this body (1) has the shape of a hollow cylinder, the side wall of which has a bulge with convex curvature.  10. Device according to claim 1, characterized in that two mechanical elements (30, 31) rotating relative to each other have two opposite cylindrical surfaces; the body (1) being of annular shape and inserted between these two bearing surfaces.  11. Device according to claim 1, characterized in that this body has the shape of a solid cylinder whose side wall has a bulge with convex curvature.  12. Device according to claim 11, characterized in that this body makes the sealed junction of a cylindrical orifice via its side wall.  13. Device according to claim 11, characterized in that this body performs the sealed junction of a cylindrical orifice through the bottom of its envelope.